The parafermionic observable satisfies a very special property first observed in [1]} (see also [2]} for a statement with a similar notation).
For every vertex of \(\Omega ^\diamond \)  with four incident edges in \(\Omega ^\diamond \) ,
\(\sum _{i=1}^4 \eta (e_i) F(e_i) = F(e_1) - {\rm i}F(e_2) - F(e_3) + {\rm i}F(e_4) = 0,\) 
